(logic) (of an inference or argument) having premises and conclusion so related that whenever the former are true the latter must also be true, esp (formally valid) when the inference is justified by the form of the premises and conclusion alone. Thus Tom is a bachelor; therefore Tom is unmarried is valid but not formally so, while today is hot and dry; therefore today is hot is formally valid Compare invalid2 (sense 2)

valid

adj.

1570s, "having force in law, legally binding," from Middle French valide, from Latin validus "strong, effective," from valere "be strong" (see valiant). The meaning "supported by facts or authority" is first recorded 1640s.